A liquid crystal display device including pixel memories (i.e., a memory-type liquid crystal device) carries out a display (memory operation mode) by temporarily retaining image data written to each pixel and carrying out a refresh operation while inverting the polarity of the image data. In a normal operation (normal operation mode, multi-color display mode) of carrying out a multi-color (multi-tone) display, new image data is written to each pixel via a data signal line every single frame. In the memory operation mode, on the other hand, image data retained in each memory circuit (pixel memory) is used, which makes it unnecessary to supply the data signal line with image data for rewriting while carrying out the refresh operation (i.e., during the time that a still image is being displayed).
This makes it possible to, in the memory operation, stop the operation of a circuit that drives the data signal lines (and, in some cases, scanning signal lines, too), thus making it possible to cut electric power consumption, and also makes it possible to reduce electric power consumption through a reduction in the number of times the large-capacity data signal lines are charged and discharged and through the elimination of the need to transmit, to a controller, image data corresponding to a memory operation period. Therefore, the memory operation mode is often used for still-image displays of which a reduction in electric power consumption is strongly required, e.g., for standby screen displays for mobile phones.
Patent Literature 1 discloses a memory-type liquid crystal display device including an inverter circuit in each pixel and two switching elements each constituted by a thin-film transistor (hereinafter abbreviated as “TFT”).